Wireless communication systems are widely deployed to provide various types of communication services such as voice or data services. A general wireless communication system is a multiple access system that can support communication with multiple users through access to available shared system resources (bandwidth, transmit power, etc.). As examples of such a multiple access system, there exist a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system and a multi-carrier frequency division multiple access (MC-FDMA) system, etc. In a wireless communication system, a terminal may receive information from a base station via a downlink (DL), and transmit information to the base station on an uplink (UL). The terminal transmits or receives information such as data and various control information, and there exist a variety of physical channels in accordance with the types and uses of the information transmitted or received by the terminal.
As a channel between a transmitting end and a receiving end is not fixed in a wireless mobile communication system, the channel between a transmitting antenna and a receiving antenna requires frequent measurement. When an agreed signal is transmitted/received between the transmitting end and the receiving end so as to measure the channel, an amount of amplitude reduction and a phase shift value caused by the channel can be detected, and the thus-detected information can be fed back to the transmitting side. Otherwise, the detected information can be used to reliably detect data information which is not agreed and decode the detected data information. The agreed signal between the transmitting end and the receiving end may refer to a reference signal, a pilot signal or a sounding reference signal.
As an example of a mobile communication system to which the present invention can be applied, a 3rd Generation Partnership Project Long Term Evolution (3GPP LTE, hereinafter, referred to as “LTE”) mobile communication system will be roughly described.
FIG. 1 illustrates an example of a mobile communication system, in which an E-UMTS network configuration is schematically shown. Evolved Universal Mobile Telecommunications System (E-UMTS) has evolved from an existing Universal Mobile Telecommunications System (UMTS), and basic standardization is underway in the 3GPP. Generally, E-UMTS may be referred to as a long term evolution (LTE) system. For a detailed description on the technical specifications of UMTS and E-UMTS, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network Release 7 and Release 8 can be referred to.
Referring to FIG. 1, E-UMTS includes user equipment (UE) 120, base stations (eNode B;eNB) 110a and 110b, and access gateways (AGs) located at an end point of a network (i.e., E-UTRAN) and connected to an external network. The base station may transmit multiple data streams at one time for a broadcast service, a multicast service and/or a unicast service.
At least one cell exists per base station. Each cell is set to one of bandwidths of 1.25, 2.5, 5, 10, 15 and 20 Mhz, and provides a downlink or uplink transmission service to each terminal. Different cells can be set to provide different bandwidths. Each base station controls data transmission/reception to/from a plurality of terminals. For downlink (DL) data, each base station transmits downlink scheduling information to relevant terminals so that the terminals can receive information regarding a scheduled time for data transmission/frequency domain, encoding, data size and hybrid automatic repeat request (HARQ). For uplink (UL) data, each base station transmits uplink scheduling information to relevant terminals so that the terminals can receive information on an available time slot/frequency domain, encoding, data size and hybrid automatic repeat and request (HARQ). An interface for transmission of user traffic or control traffic can be used between base stations. A core network (CN) can be constituted by network nodes for AGs and user registration of a terminal. AGs manage the mobility of the terminal on the basis of tracking areas (TAs) which consist of a plurality of cells.
Wireless communication techniques have now been developed to LTE based upon WCDMA, however, level of requests and expectation of users and enterprises are steadily increasing. Moreover, other wireless access techniques are continuously being developed, and therefore, evolution to new techniques is required for future competitiveness. In this context, per-bit cost reduction, increase in service availability, flexible use of frequency band, simple configuration, open interface and appropriate power consumption of a terminal are required.
Recently, progress has been made by 3GPP in standardization for the technique to supersede LTE. This technique will be referred to as “LTE-Advanced” or “LTE-A” throughout this description. One of the main differences between an LTE system and an LTE-A system is system bandwidth. The LTE-A system aims to support a broadband of a maximum of 100 MHz. For this, the LTE-A system employs carrier aggregation or bandwidth aggregation which uses a plurality of frequency blocks to achieve broadband. Carrier aggregation uses a plurality of frequency blocks as a single large logical frequency band so as to use a wider frequency band. The bandwidth of each frequency block can be defined based on the bandwidth of the system block used in the LTE system. Each frequency block is transmitted using a component carrier.